MOLECULAR MECHANISM OF PUX1 INHIBITION OF GIBBERELLIN SIGNALING AND PLANT GROWTH

Gibberellin (GA) hormone signaling promotes numerous developmental processes of agronomic importance including seed germination, growth, and transition to flowering. The major goal of this project is to investigate the molecular mechanism underlying PUX1 regulation of GA signaling, to control plant growth and development. The major GA response pathway relies of the degradation of DELLA proteins, a family of transcription regulators, by GA-activated GIBBERELLIN-INSENSITIVE DWARF1 (GID1) receptors. We have recently identified Plant (UBX) domain-containing Protein 1 (PUX1) as a negative regulator of GA signaling and/or biosynthesis. PUX1 interacts with the GA receptor, GID1 and recruits the molecular chaperone, AtCDC48A to form a complex. PUX1 may therefore control growth and development via GID1-PUX1-CDC48A complex interaction with DELLAs and other components of the GA response pathway. Preliminary data have suggested that GA regulates the post-translational processing of PUX1. However, the nature post-translational modifications and the mechanisms by which they modulate GA homeostasis and the GA response, potentially through control of GID1 and DELLA degradation, remains to be defined. To address this, we will use a combination of biochemical and genetic approaches in the model plant Arabidopsis thaliana to further investigate the mechanisms by which PUX1 negatively regulates GA responses via regulating DELLA and GID1 protein levels. Furthermore, we will identify whether PUX1 modulates GA levels by specifically regulating the biosynthesis and/or catabolism of GA. The chemical nature of the post-translational modification of PUX1 will be determined, as well as their role in altering its localization and function in GA signaling. RELEVANCE: This study will enhance our understanding of the interaction of PUX1 with the machinery involved in DELLA-dependent GA signaling. It will identify whether PUX1 modulates GA levels by specifically regulating the biosynthesis and/or catabolism of GA. Additionally, the studies will also explore whether GA-signaling modulate PUX1 post-translational modification and determine if the post-translational modification of PUX1 is likely of biological significance for its localization and/or function. Insight into how PUX1 regulates GA signaling could lead to the development of new strategies for the generation of crops with enhanced yield and quality for sustainable food, feed-stock and bio-fuel production. The specific objectives of this project are as follow:Determine whether PUX1 negatively regulates GA synthesis and/or distribution in plantaExamine DELLA and GID1 expression and degradation in pux1 mutantsDetermine whether full length PUX1 undergoes post-translationally modificationFunctional analysis of PUX1 nucleocytoplasmic localization